linux-kernel - Re: [PATCH v6 5/5] mfd: max77541: Add ADI MAX77541/MAX77540 PMIC Support

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Date:   Thu, 30 Mar 2023 10:07:03 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Lee Jones <lee@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     "Sahin, Okan" <Okan.Sahin@...log.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Cosmin Tanislav <demonsingur@...il.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Caleb Connolly <caleb.connolly@...aro.org>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        "Bolboaca, Ramona" <Ramona.Bolboaca@...log.com>,
        ChiYuan Huang <cy_huang@...htek.com>,
        "Tilki, Ibrahim" <Ibrahim.Tilki@...log.com>,
        William Breathitt Gray <william.gray@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        ChiaEn Wu <chiaen_wu@...htek.com>,
        Haibo Chen <haibo.chen@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>
Subject: Re: [PATCH v6 5/5] mfd: max77541: Add ADI MAX77541/MAX77540 PMIC
 Support

On 30/03/2023 10:04, Krzysztof Kozlowski wrote:
> On 29/03/2023 17:06, Lee Jones wrote:
>> On Wed, 29 Mar 2023, Lee Jones wrote:
>>
>>> On Wed, 29 Mar 2023, Andy Shevchenko wrote:
>>>
>>>> On Wed, Mar 29, 2023 at 03:36:15PM +0100, Lee Jones wrote:
>>>>> On Tue, 28 Mar 2023, Sahin, Okan wrote:
>>>>>>> On Wed, 15 Mar 2023, Lee Jones wrote:
>>>>>>>> On Tue, 07 Mar 2023, Okan Sahin wrote:
>>>>
>>>> ...
>>>>
>>>>>> +static const struct i2c_device_id max77541_i2c_id[] = {
>>>>>> +	{ "max77540", (kernel_ulong_t)&chip[MAX77540] },
>>>>>> +	{ "max77541", (kernel_ulong_t)&chip[MAX77541] },
>>>>>
>>>>> Just 'MAX77540' is fine.
>>>>
>>>> I tend to disagree.
>>>>
>>>> There is an error prone approach esp. when we talk with some functions
>>>> that unifies OF/ACPI driver data retrieval with legacy ID tables.
>>>> In such a case the 0 from enum is hard to distinguish from NULL when
>>>> the driver data is not set or not found. On top of that the simple integer
>>>> in the legacy driver data will require additional code to be added in
>>>> the ->probe().
>>>
>>> Use a !0 enum?
>>>
>>> The extra handling is expected and normal.
>>
>> I've always disliked mixing platform initialisation strategies.  Passing
>> pointers to MFD structs through I2C/Device Tree registration opens the
>> doors to all sorts of funky interlaced nonsense.
>>
>> Pass the device ID and then match in C-code please.
> 
> I agree. Especially that casting through ulong_t drops the const, so the
> cast back needs const which can be forgotten. The patch already makes
> here mistake!

Uh, no, the code is correct - chip_info member is const. Yet it is a
mistake easy to make for the device ID tables using void * or ulong.

Best regards,
Krzysztof